The invention is directed to a laser video projection system, and more particularly to a laser video projection system for digital motion pictures that thwarts recording of the projected image with a camcorder or an electronic camera.
Piracy and illegal copying of digital audio and video material has become widespread with the availability of inexpensive CD and DVD burners. This threatens the existence of record labels and of movie studios and motion picture distributors. One way of producing illegal copies is to intercept file content from a legal copy of copyrighted work, either by making an illegal copy of a CD/DVD or by intercepting data transferred, for example, from a movie studio to a movie theater intended for digital projection. This process requires some skill on the part of the copyright infringer. Moreover, making illegal copies from CD/DVD may become unworkable due to security features added to the original recording.
Another albeit less sophisticated way of copying movies is to record a projected movie directly from the projection screen in a movie theater with an electronic camera, for example, a CCD camera that can be analog or digital. In current film-based projectors, a movie is projected frame-by-frame, and a blanking period (dark screen) of less than few ms duration exists in regular interval, which is not perceived by the human eye. However, camcorders with a response time in the order of microseconds record during the brief moment the projector light is blocked an objectionable black stripe that moves across the picture. Consequently, such recordings have little commercial value and are mainly found in countries where recordings are sold based on price alone, without regard for the quality of the recording.
There is an increased emphasis to record, transmit and project images digitally. Digital projection systems emit a continuous stream of light, so that images projected with digital projection systems do not include such blanking periods and can therefore readily be recorded by a pirate using a camcorder. Since there may be no perceivable image degradation, the pirate may produce an illegal copy with a CD burner and sell these copies to a wide market at a substantial profit. This is a big concern for the movie studios, in particular in view of the conversion to digital cinema, which includes digital projection.
Digital projection systems presently use lamp-based systems with LCD light valves or deformable mirrors (DMD), or alternatively laser-based systems. LCD-based systems, especially the one using LCoS (Liquid Crystal on Silicon) panels, are relatively slow, with response times of 5–12 ms, so that any intentionally introduced blanking period will be comparable to the response time of the human eye and hence also be perceived by an observer. The response (rise+fall) time of DMD-based systems is approximately 20–50 μs, and at least one proposed anti-piracy system superimposes on the deformable mirrors a random pattern of approximately 1 ms duration. The resulting distortion of the projected image is not perceived by the human eye, but produces an objectionable image pattern in a movie recorded off a projection screen.
For the reasons stated above, it would therefore be desirable to incorporate anti-piracy features in a laser-based movie projection system that can thwart recording of a digitally projected movie from the projection screen by a camcorder or other type of electronic camera.